Horizontal coordinates in terms of the NZGD1949 are classified into horizontal orders according to the type and standard of observations that were used to determine them. A numerically lower order generally implies a more reliable coordinate.
The following table describes the NZGD1949 Orders. A description of the NZGD1949 observations standards is described in the next table.
|1||Coordinates derived from the original NZGD1949 adjustment in 1949 that defines the datum. The observations meet the 1st order observation standards|
|2||Coordinates derived from adjustments of observations of 2nd order observation standards connecting to 1st order marks|
|3||Coordinates derived from adjustments of observations of 3rd order observation standards connecting to 1st or 2nd order marks|
|4a||Coordinates from 2nd or 3rd order control downgraded because of poor design, high density, substandard ground marking, large adjustment corrections or non-compliance with 2nd or 3rd order specifications.|
|4b||Coordinates supplied by LINZ District Office or LINZ contractors from modern reliable survey fix with proven origin and observation specifications (benchmark coordinates derived from urban or rural geodetic control surveys, trig coordinates derived from photo control surveys)|
|4c||Coordinates determined by a hanging line fix over 100m long from a 1st, 2nd or 3rd order station or benchmarks with geodetic coordinates obtained from unknown sources|
|4h||NZGD1949 coordinates obtained by double entry table transformation from initial coordinates in terms of the Hawkes Bay 1931 datum (post-Napier earthquake)|
|5||Old Cadastral datum coordinates adjusted using the original triangulation field data|
|6a||Old cadastral datum coordinates converted to NZGD1949 by double entry table transformation|
|6b||Coordinates obtained by scaling from maps|
|2d, 3d, 4d||Coordinates calculated in terms of NZGD2000 and subsequently transformed to NZGD1949.
These coordinates may be inconsistent with surrounding NZGD1949 coordinates as they were often measured from remote marks using GPS. The transformation modelled some of the distortion in the NZGD1949 datum, but it cannot represent all local effects.
NZGD1949 'd' coordinates are also described on this site.
NZGD1949 Observation standards
The NZGD1949 datum is largely derived by adjustments of triangulation (horizontal angle) data. The following minimum standards were required for deriving 1st, 2nd, and 3rd order coordinates.
|Order||Triangle Closure||Length Closure||Number of Sets|
|1||1"||3"||1 in 25,000||12|
|2||3"||5"||1 in 10,000||6|
|3||5"||8"||1 in 5,000||3|